1. Field of the Invention
The present invention relates generally to methods and devices for use in performing pulmonary procedures, and more particularly, procedures for treating various diseases of the lungs.
2. Description of the Related Art
Pulmonary diseases such as emphysema and chronic obstructive pulmonary disease (COPD) reduce the ability of one or both lungs to fully expel air during the exhalation phase of the breathing cycle. The diseased lung tissue is less elastic than healthy lung tissue, which is one factor that prevents full exhalation of air. During breathing, the diseased portion of the lung does not fully recoil due to the tissue being less elastic. Consequently, the diseased (e.g., emphysematic) lung tissue exerts a relatively low driving force, which results in the diseased lung expelling less air volume than a healthy lung. The reduced air volume exerts less force on the airway which allows the airway to close before all air has been expelled, another factor that prevents full exhalation.
The problem is further compounded by the diseased, less elastic tissue that surrounds the very narrow airways that lead to the alveoli (the air sacs where oxygen-carbon dioxide exchange occurs). This tissue has les tone than healthy tissue and is typically unable to maintain the narrow airways open until the end of the exhalation cycle. This traps air in the lungs and exacerbates the already-inefficient breathing cycle. The trapped air causes the tissue to become hyper-expanded and no longer able to effect efficient oxygen-carbon dioxide exchange. Applying suction to these narrow airways (a procedure proposed in the literature for deflating the diseased portion of the lung) may collapse the airways due to the surrounding diseased tissue, thereby preventing successful fluid removal.
In addition, hyper-expanded lung tissue occupies more of the pleural space than healthy lung tissue. In most cases, a portion of the lung is diseased while the remaining part is healthy and therefore still able to efficiently carry out oxygen exchange. By taking up more of the pleural space, the hyper-expanded lung tissue reduces the amount of space available to accommodate the healthy, functioning lung tissue. As a result, the hyper-expanded lung tissue causes inefficient breathing due to its own reduced functionality and because it adversely affects the functionality of adjacent healthy tissue.
Lung reduction surgery is a conventional method of treating lung diseases such as emphysema. A diseased portion of the lung is surgically removed which makes more of the pleural space available to accommodate the functioning, healthy portion of the lung. The lung is typically accessed through a median sternotomy or small lateral thoracotomy. A portion of the lung, typically the upper lobe of each lung, is freed from the chest wall and then resected, e.g., by a stapler lined with bovine pericardium to reinforce the lung tissue adjacent the cut line and also to prevent air or blood leakage. The chest is then closed and tubes are inserted to remove air and fluid from the pleural cavity. The conventional surgical approach is relatively traumatic and invasive, and, like most surgical procedures, is not a viable option for all patients.
More recently proposed treatments include the use of devices that employ RF or laser energy to cut, shrink or fuse diseased lung tissue. Another lung volume reduction device utilizes a mechanical structure that is used to roll the lung tissue into a deflated, lower profile mass that is permanently maintained in a compressed condition. As for the type of procedure used, open surgical, minimally invasive and endobronchial approaches have all been proposed. Another proposed device (disclosed in publication no. WO 98/48706) is positioned at a location in the lung to block airflow and isolate a part of the lung. The publication states that the occlusion device is introduced through an endobronchial delivery device, and is resiliently deformable in order to provide a complete seal against airflow.
The search for new and better treatments underscores the drawbacks associated with existing pulmonary procedures. Accordingly, there is a need in the art for improved methods and devices for performing pulmonary procedures, and in particular, treating lung diseases such as emphysema.